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KVM: arm64: Ignore writes to PMCR_EL0.N when using strict UAPI

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KVM allows userspace to configure the number of event counters by
writing to PMCR_EL0.N. While this makes a bit of sense prior to NV, the
value of the field is context-dependent whether or not the vCPU is at
EL2 or EL1. As such, the vCPU attribute was added afterwards and made
mandatory for NV.

As we're in the process of papering over old mistakes, force userspace
to use the vCPU attribute if KVM_ARM_VCPU_PMU_V3_STRICT is set.

Reviewed-by: Geoff Blake <blakgeof@amazon.com>
Reviewed-by: Haris Okanovic <harisokn@amazon.com>
Signed-off-by: Congkai Tan <congkai@amazon.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20260722202702.4165917-4-congkai@amazon.com
Signed-off-by: Oliver Upton <oupton@kernel.org>
This commit is contained in:
Oliver Upton 2026-07-22 20:27:01 +00:00
parent 203b22f76d
commit bbef6317f9
1 changed files with 1 additions and 0 deletions
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1
arch/arm64/kvm/sys_regs.c
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@ -1502,6 +1502,7 @@ static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
*/
if (!kvm_vm_has_ran_once(kvm) &&
!vcpu_has_nv(vcpu) &&
!kvm_vcpu_has_pmuv3_strict(vcpu) &&
new_n <= kvm_arm_pmu_get_max_counters(kvm))
kvm->arch.nr_pmu_counters = new_n;